Shuzo Oshima

Effect of non-Newtonian property of blood on flow through a stenosed tube

It is well known that the fluid dynamics of arterial blood flow plays an important role in arterial diseases. Periodic blood flow through a stenosed tube was analyzed numerically. The bi-viscosity model is used as a constitutive equation for blood, and the flow is assumed to be periodic, incompressible and axisymmetric. Effects of pulsation and the rheological property of blood are considered. The flow pattern, separated region and the distributions of pressure and shear stress at the wall are obtained. The results show that the non-Newtonian property reduces the strength of the vortex downstream of stenosis and has considerable influence on the flow even at high Stokes and Reynolds numbers, provided that pulsatile flow has a stagnant period.

Classification of Pulsating Flow Patterns in Curved Pipes

The fully developed periodic laminar flow of incompressible Newtonian fluids through a pipe of circular cross section, which is coiled in a circle, was simulated numerically. The flow patterns are characterized by three parameters: the Womersley number Wo, the Dean number De, and the amplitude ratio beta. The effect of these parameters on the flow was studied in the range 2.19 < or = Wo < or = 50.00, 15.07 < or = De < or = 265.49 and 0.50 < or = beta < or = 2.00, with the curvature ratio delta fixed to be 0.05. The way the secondary flow evolved with increasing Womersley number and Dean number is explained. The secondary flow patterns are classified into three main groups: the viscosity-dominated type, the inertia-dominated type, and the convection-dominated type. It was found that when the amplitude ratio of the volumetric flow rate is equal to 1.0, four to six vortices of the secondary flow appear at high Dean numbers, and the Lyne-type flow patterns disappear at beta > or = 0.50.

Vortex enhancement in blood flow through stenosed and locally expanded tubes

It is well known that fluid dynamical phenomena in arterial blood flow can play an important role in arterial diseases. Periodic blood flow through stenosed and locally expanded tubes is analyzed numerically. The fluid is assumed to be non-Newtonian and incompressible, and the flow is assumed to be periodic in time and axisymmetric. It is found that the vortex downstream of stenosis or expansion becomes strongest at a certain frequency of pulsation. This phenomenon is called vortex enhancement in this paper. The flow pattern, separated region and the distributions of pressure and shear stress on the wall are obtained. The results show that the vortex enhancement occurs in both tubes. The vortex enhancement occurs where the difference between the adverse pressure and the friction on the wall is a maximum.

Oscillation of a diamagnetic liquid bubble suspended by magnetic force

Abstract The levitation of the diamagnetic liquid droplet with the strong magnetic field is experimentally simulated, using the magnetic fluid as the surrounding fluid in place of air or gas, and the water bubble is levitated with the conventional permanent magnet. When the stepwise magnetic field is superposed, the suspended bubble behaves as a typical step response with the overshoot and viscous damping. The effects of the volume of the bubble, the strength of the magnetic field and the concentration of the magnetic fluid are investigated.

The position control of a capsule filled with magnetic fluid

In this paper, in order to establish the technique of a nozzle-flapper system of a servo valve using magnetic fluid in hydraulic system, a governing equation regarding the levitation of a capsule filled with magnetic fluid is formulated. Using PID control, an experiment for the position control of a capsule was performed. The experimental results were compared with the simulation results found by the governing equation.

Axial oscillation of a magnetically levitated non-magnetic fluid column inside a straight magnetic pipe

The axial oscillation of a magnetically levitated non-magnetic liquid column in a magnetic fluid and a non-uniform weak magnetic field is studied theoretically and experimentally. The angular speed equation and wave speed equation of the interfacial wave are derived from the ferrohydrodynamics Navier–Stokes equation in a given magnetic field by (1) omitting the non-linear terms, (2) assuming that the undisturbed interface between the levitated fluid and the surrounding fluid is an infinite long cylindrical surface, and (3) assuming that the disturbance is an axisymmetric axial one of small amplitude. The experimental study is made by setting two very long permanent magnetic north poles face to face with each other to form the non-uniform magnetic field, using silicon oil as the levitated fluid and using a diluted water-based magnetic fluid as the surrounding fluid.

A study on autobalancing of a casing oscillator using feedback control

The casing oscillator used for basic construction of buildings, factories, and bridges is a construction machine which rotates and rolls the casing to insert it into the ground. It is very important that the casing is retained at a perpendicular position to sea level regardless of the slope of ground. In this paper, we present a new casing oscillator that does need not to be level to the ground for the casing insertion to work. The kinematic analysis for work space of a casing oscillator is presented and carried out with autobalancing of the casing oscillator using feedback control.

Local velocity measurement of magnetic fluid flow using laser optical fiber sensor

Abstract The local velocity of an open channel flow of magnetic fluid in a traveling magnetic field is measured using a laser optical fiber sensor. The measured velocity distributions are compared with the theoretical ones. The shapes of the distributions are quite different from those of nonmagnetic fluid flow.

Interfacial waves of the magnetic fluid in vertical alternating magnetic fields

Abstract The stability of the surface of a magnetic fluid layer under the influences of vertical alternating magnetic fields was investigated experimentally and analytically. Two kinds of waves were excited on the surface and the critical conditions for the onset and the wavelength of these waves were obtained.

Coherent structure in the turbulent wake behind a circular cylinder 2. Numerical simulation using the vortex filament model

In the previous paper the authors reported observing the formation of a spoon-shaped vortex chain in a wake behind a circular cylinder as a coherent structure in turbulence. In this report numerical simulation is carried out based on the assumption that the structure is formed by deformation of the Kannan vortices. The basic equation is the localized induction equation for a single vortex filament with an influence of the background mean flow. The vortex filament is given an initial deformation within a plane at an angle θ to the x–z plane (x is the mean flow direct and z the spanwise direction) with the width Zw, and the further deformation process of the filament is numerically traced. The first calculation is made with fixed Zw and various values of θ. The result shows that the vortex filament finally reaches a structure lying on a plane with a constant angle of 30° ~ 45° to the x-z plane irrespective of the initial values of θ. The second calculation is made with fixed θ and various values of Zw. In this case the final spanwise scale of the deformed region of the filament has almost constant values of about 4d–6d (d is diameter of the cylinder). These results indicate that the final structure of the vortex filament is stable and definite irrespective of the initial disturbances.